Recently, from the perspective of environmental protection, a wind turbine generator using wind power and other wind turbine generator using renewable energy such as tidal current, ocean current and river current are becoming popular. In the renewable-energy type power generating apparatus, motion energy of wind, tidal current, ocean current or river current is converted to rotation energy of the rotor and the rotation energy is converted to electric power by a generator.
This type of power generating apparatus requires a step-up gear between the rotor and the generator as the rotation speed of the rotor is smaller than the rated rotation speed of the generator. Specifically, the rotation speed of the rotor is increased by the step-up gear to the rated rotation speed of the generator and then inputted to the generator.
To improve power generation efficiency, the power generating apparatus of renewable energy type becomes larger to improve power generation efficiency and the step-up gear becomes heavier and more expensive as well. In view of this, a power generating apparatus of renewable energy type which uses hydraulic transmission having a hydraulic pump and a hydraulic motor instead of the mechanical step-up gear, receives increased attention.
For instance, the wind turbine generating apparatus with the hydraulic transmission is disclosed in Patent Document 1 and Patent Document 2. The wind turbine generating apparatus with the hydraulic transmission has the hydraulic pump installed around the main shaft and the hydraulic motor driven by pressure oil from the hydraulic pump. This wind turbine generating apparatus drives the hydraulic pump by the rotation of the main shaft, rotates the hydraulic motor by the pressure oil supplied from the hydraulic pump and drives the generator by the rotation of the hydraulic motor.